Wood Destroying Insects in Buildings Insect Pests of Converted Timber The more important insect pests, the larvae of which attack felled and converted timber, are beetles of the genera ANOBIIDAE, LYCTIDAE, CERAMBYCIDAE, CURCULIONIDAE and SCOLYTIDAE. They are very numerous and extremely varied in their general appearance and feeding habits. They include some of the largest and most minute of adult insects, but relatively few species infest converted timber in the UK. The larvae of some beetles, such as LYCTIDAE AND BOSTRYCHIDAE, derive their nourishment from the starch or other carbohydrates which are present in the sapwood cells of wood for some time after the trees are felled. Others, such as the Common furniture beetle of the genus Anobium and the Death watch beetle, genus Xestobium, actually feed on the wood substance, consuming the cellulose and other constituents of the cell walls. Preventive Measures Attack by any of the wood-destroying beetles found in the UK can be prevented by adequate treatment of the wood, with an approved insecticide/biocide. Pressure ‘pre-treatment’ gives the maximum protection to any timber. Dipping, brushing and spraying with a suitable insecticide/biocide can give effective protection if the preservative is thoroughly applied and the surfaces are clear of dust. COMMON FURNITURE BEETLE - Anobium punctatum The Common furniture beetle naturally inhabits dead stumps and fallen branches in woods and hedgerows, but is more abundant in building timbers and furniture and is the most common of the wood destroying insects found in buildings in the UK. Most damage is found in timber which has been in use for 10 years or more. Description of the Beetle The adult beetles are 2.5mm-5mm in length and are reddish to blackish brown in colour. The first body segment (prothorax) is hood-shaped and when viewed from above almost completely hides the head. The upper parts of the body are clothed with a fine covering of short yellow hairs, and rows of small pits or punctures on the wing cases are well defined. The females lay eggs in grooves on the surface of the wood, in joints which have opened slightly, or on the surface where the grain has been torn in machining. The eggs hatch into white larvae having six minute legs and when mature are about 6mm long. The terminal segment of the larva is rather bulbous and the whole larva is bent into a crescent shape. As the larvae feed on the wood they bore galleries which become partly filled with granular wood bore dust (frass), similar to fine sand. When fully developed, after 3 – 5 years, the larvae approach the surface of the timber and pupate. After the pupation period, the adult beetles bore small round exit holes about 1.5mm in diameter. The adult beetles are capable of flight and this enables them to travel and infest other timbers. In the period from March to September, adults can be found on the window ledges of houses containing infested timber. Treatment 1. All timber should be investigated to determine evidence of current activity to justify any form of treatment. Some timbers may show signs of historic activity however the insect may be extinct due to unsuitability of the timber, decreased moisture content or due to previous treatments whereby re-treatment is not justified. 2. Furniture and small wooden articles may be ‘target’ treated by brush or hand-spray using a preparatory ‘amateur’ use approved insecticide/biocide. 3. The most convenient way of treating infested timber whether in furniture or in buildings, is by the application of an approved insecticide/biocide solution to all parts showing signs of infestation, as well as to the adjacent timbers. Special attention should be paid to the undersides and surfaces with limited accessibility whether in furniture or in structural timbers and all surfaces should be evenly treated. With structural timbers, dust and dirt should be cleaned off and floor coverings, such as carpets and linoleum, should be removed so as to give access to the timber. The beetle does not lay eggs on painted or polished surfaces but may use old flight holes. 4. Where the attack is so severe that the strength of the timber is affected it may be necessary to replace the infested parts with new timber which should be treated before use. 5. The most effective time for application of insecticides is from early Spring to late Summer when adults emerge. 6. The insecticide may be applied by brush or coarse low pressure spray. 7. In some circumstances the use of fumigation, heat or freezing techniques can be considered. These procedures must be conducted by properly trained and competent technicians. 1 DEATH WATCH BEETLE – Xestobium rufovillosum The natural habitat of the Death watch beetle is in decayed parts of old trees, especially willows and oaks. In buildings, timber which is free from decay is rarely, if ever, attacked, the eggs being laid almost invariably in decayed parts of the timber. The larval period is influenced by the extent of decomposition resulting from fungal activity although the average length of the life cycle is 4 – 5 years but can extend to 10 years. The condition of the wood appears to be important both to the Common furniture beetle and the Death watch beetle, sometimes infested wood will become deserted due to changes in the condition of the timber or the action of predatory insects. Death watch beetles prefer to infest decayed hardwoods (although softwoods are not immune) therefore infestations are less commonly found than those due to the Common furniture beetle. The larger larval size and the longer larval period results in more serious infestations which can lead to breakdown in structural timbers that may then require replacement. In churches and other older buildings damage by both Death watch and Common furniture beetles may be present in the same timber component. Description of Beetle The Death watch beetle, the largest of the genus ANOBIIDAE family of insects, measures from 5mm-8mm in length. Its colour is dark chocolate brown with patches of short yellowish hairs, which give the insect a variegated appearance. In old specimens these hairs may have been rubbed off, in which case the mottled appearance is less obvious. The eggs, which are white, lemon-shaped and measure about 0.5mm in length, are laid in open joints between adjacent timbers, in cracks or crevices in the surface of the wood, and sometimes within old tunnels and exit holes. The larvae are curved and white, covered with long fine yellowish hairs and are over 6mm in length. The phases of the life cycle are the same as for the Common furniture beetle, but the beetles commonly emerge in April, May or June, leaving a round exit hole about 3mm in diameter. Infestations by Death watch beetle can easily be distinguished from that of other wood boring insects by the presence of small bun-shaped pellets in the bore dust (frass) produced by the larvae. Treatment Timber infested by the Death watch beetle should be very carefully inspected, before any treatment is undertaken. Such inspection should, if possible, take place during the period April to June whilst the beetles are emerging. The source of moisture that encourages fungal decay and continuation of the infestation should be removed and the timber dried out. Treatment with an insecticide by brush or spray during the emergence period of the beetle is useful in destroying eggs and young larvae before they enter the wood, but it is doubtful whether such treatment will kill older larvae working below the surface at any appreciable depth. The following is a summary of the recommended stages of treatment in an infested building: 1. Investigate the source of moisture that has contributed to the infestation and take measures to reduce the dampness and dry out the infected areas. 2. A competent person should determine the extent of damage and the amount of heavily infested timber that can be retained. Strengthening may be considered to avoid removal of timbers by using other materials (i.e. Resin). Determine the risk of continued activity and spread of attack unless insecticidal treatments are applied to both existing infested and replacement timber. The age of affected buildings often will require Listed Building Consent for this work. 3. Preparation by removal of bore dust and debris from timber by scraping/defrassing and the use of a vacuum cleaner to remove all loose infested timber and debris before treatment with an insecticide. 4. Two applications of an insecticide by brush or spray during the period of April to June supplemented by targeted application using an appropriate insecticidal paste. It is advised that further annual applications for at least four consecutive years are considered. 5. Search for any further evidence of infestations and damage caused by Death watch beetles to exposed timbers during treatment. 6. Ongoing monitoring of previously infested timbers should be undertaken every Spring for a period of years after treatment to detect any evidence of continued activity in the form of fresh exit-holes or bore dust, in which case continued insecticidal treatments may be necessary as long as any activity remains. New or replacement (hardwood) timber should be sound, adequately seasoned and free from sapwood which is particularly liable to attack by fungi and insects. When oak heartwood is used, treatment with a preservative is not 2 necessary. If replacing with softwoods, which are less resistant to decay, these should be pressure treated in accordance with BS8417: 2011 and any cut ends locally treated. ‘Period’ replacement timber showing evidence of even slight decay or infestations should not be used unless the user is confident the decay/infestation is extinct.